of MM. P. Curie and C. Cheneveau. 



365 



can be suspended. To this end the glass tube is closed by a 

 cork carrying a metallic ring which hangs on the hook c. 

 The tube t is therefore in a vertical position. On the other 

 end of the arm TT is fixed a copper sector, S', which moves 

 between the poles of a fixed damping magnet A. To vary 

 the sensitiveness the torsion-wire can be changed, and the 

 damping varied by the position of the copper sector in the 

 field. 



On the horizontal arm TT is fixed a vertical copper strip 

 which carries a hook to which the torsion-wire / (-^ mm. 

 platinum) is attached. Below, this strip is turned at right 

 angles as shown by the portion DE parallel to TT. Balance 

 is obtained partly by the aid of a small copper cylinder B, 

 sliding on the rod TT, when the tube is empty, and partly by 

 copper or aluminium riders, pp, to compensate for the weight 

 of the solid or liquid material which fills the tube to the level 

 marked. 



The displacement of the magnet N.S. is obtained by a 

 movement of rotation around an axis ; this movement is 

 smoother than the sliding motion of our earlier model. The 

 movements of the torsion-balance are followed by the observer 

 upon a divided scale 0. (fig. 6). For this purpose a 2-metre 



Kir. 6. 



radius concave mirror m is attached to the balance-arm, and 

 the image of a straight filament is employed. The displacement 

 of the. magnet is effected by. a controller M . (fig. 6;. fixed in 



